The reduction of fat intake by Americans has been identified as a major public health goal, since excessive consumption of fat has been linked to numerous negative health consequences including obesity, cardiovascular disease, and some types of cancer. Thus, there is compelling need to identify the behavioral mechanisms and dietary attributes which foster overconsumption (hyperphagia) of high-fat foods. The proposed studies will utilize an animal model to determine the independent and interactive contributions to oral sensations (palatability), caloric density, and the unique postingestive effects of dietary fat to the control of intake. This will be accomplished by systematically manipulating each of these variables while holding the others constant, and examining the impact on both short-term measures of ingestive behavior (meal size and postprandial satiety) and long-term (16 day) intake relative to controls fed a high-carbohydrate, low-fat diet. The use of liquid diets allows easy manipulations of dietary attributes, and also permits isolation of oral and postingestive influences on intake via the techniques of sham feeding and intragastric feeding, respectively. These methods will eliminate the confounding of dietary variables that has been unavoidable in traditional oral-feeding studies, and thus will enable an unbiased assessment of the relationship of each variable to intake. Humans exhibit individual differences in the accuracy with which caloric intake is regulated when consuming a high-fat diet, as do rats. An additional goal is to determine whether short-term measures of ingestive behavior are useful predictors of individual differences in the magnitude of high-fat diet hyperphagia. To determine whether discrete measures correlate with individual differences in the magnitude of high-diet hyperphagia, taste responsivity to fat (via sham-feeding), meal size, and postprandial satiety (via a preloading paradigm) will be obtained prior to lad lib consumption of a high-fat diet. Identification of a behavioral marker(s) for susceptibility to overeating, such as abnormally large meal size or reduced sensitivity to the satiating effect of fat, would be clinically valuable if a similar predictive relationship were then found in humans. Together, results from these studies will provide a greater understanding of how and why high-fat diets promote excessive intake and weight gain by focusing on both the specific dietary attributes that elicit overeating, and the behavioral mechanisms through which the hyperphagia is expressed. An increased understanding of the underlying determinants of high-fat diet hyperphagia has the potential to inform and positively impact clinical and public health strategies aimed at promoting a healthier level of fat intake.